• Inferior vena cava blood enters the right atrium and most of it is shunted immediately across the foramen ovale into the left atrium, left ventricle and ascending aorta, which supplies the heart, brain and arms. Only a small amount of it is, distributed through the tricuspid valve to the right ventricle. • The returning blood from the upper part of the body enters the right atrium through the superior vena cava and then passes into the right ventricle. Because pulmonary arteriolar vasoconstriction maintains high resistance in the pulmonary circuit, most main pulmonic blood from the right ventricle traverses the ductus arteriosus to the descending aorta, rather than to the branch pulmonary arteries and lungs. The right ventricle, therefore, provides blood to the descending aorta which supplies the abdomen and legs, finally, returning to the placenta. • So the concentration of oxygen is the highest in the liver, next is the upper part of the body and the last is the lower part of the body.
